Oxygen separators such as disclosed in U.S. Pat. No. 3,880,616, separate fluid mixtures into first and second component parts through the retention of one component in a bed of adsorption material while allowing the other components to flow therethrough. In order to provide for continuous operation, it is common practice to use two beds of adsorption material simultaneously, adsorbing one bed while desorbing the other bed. A first series of solenoid valves associated with the two beds allow the fluid mixture to freely flow to a first of the two beds where one component is retained while a product effluent flows to a storage container through a conduit. At the same time a portion of the product effluent enters a second of the two beds and purges the same of the one component previously retained therein. After a fixed period of time, a signal from a timing mechanism deactivates the first series of solenoid valves and activates a second series of solenoid valves to reverse the communication of the fluid mixture from the first of the two beds to the second. The first bed of adsorption material previously producing the product effluent is now purged by a portion of the product effluent produced in the second bed.
Theoretically, the volume of fluid mixture passing through the first and second beds of adsorption material should be equal. However in practice it has been observed that the beds of adsorption materials are nearly always different. Such difference can result from minute changes in size between the beds, variations in the density of the beds, and variations in the quality of the beds such as porosity and moisture content. In addition, a few seconds change in the operation of the solenoid control valves by the timing mechanism can cause a degradation of the beds.
Thus, one of the two beds is always producing more of a product effluent than the other. The overproducing bed experiences a component breakthrough which dilutes the product effluent during its adsorption part of the operational cycle while the underproducing bed has an excessive amount of the component retained therein at the initiation of its adsorption cycle. The underproducing bed never reaches its output potential since the adsorption cycle is terminated before the product effluent output peaks.
One method of providing identical beds requires the testing of the adsorption capacity of the beds as they are produced and thereafter selecting matching beds of the same capacity for each unit. Unfortunately, this type of quality control does not lend itself for rapid manufacturing production.
Another method of acquiring optimum output from an oxygen separator requires the use of an electrical timer whereby the operation of the solenoid control valves can be varied to match the adsorption capacity of the beds. The underproducing bed cycle of adsorption is lengthened while the overproducing bed cycle is shortened until both beds are operating at top efficiency. However, this solution is only temporary since after an extended period of time the beds become unbalanced in the opposite direction since the retained component is never completely purged from the one bed.
In copending U.S. patent application Ser. No. 784,901 filed Apr. 5, 1977 and now U.S. Pat. No. 4,101,298, a pneumatic logic sequencer is disclosed for controlling the transfer of the pressurized fluid mixture between the first and second beds of adsorption material. A first pressure sensor connected to the first bed of adsorption material and a second pressure sensor connected to the second bed of adsorption material supply the logic sequencer a pneumatic signal representative of the fluid pressure in the first and second beds of adsorption material, respectively. In response to a predetermined pressure differential, the logic sequencer transfers the pressurized fluid mixture to the bed of adsorption material having the lower fluid pressure.